Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * auth-scram.c
4 : * Server-side implementation of the SASL SCRAM-SHA-256 mechanism.
5 : *
6 : * See the following RFCs for more details:
7 : * - RFC 5802: https://tools.ietf.org/html/rfc5802
8 : * - RFC 5803: https://tools.ietf.org/html/rfc5803
9 : * - RFC 7677: https://tools.ietf.org/html/rfc7677
10 : *
11 : * Here are some differences:
12 : *
13 : * - Username from the authentication exchange is not used. The client
14 : * should send an empty string as the username.
15 : *
16 : * - If the password isn't valid UTF-8, or contains characters prohibited
17 : * by the SASLprep profile, we skip the SASLprep pre-processing and use
18 : * the raw bytes in calculating the hash.
19 : *
20 : * - If channel binding is used, the channel binding type is always
21 : * "tls-server-end-point". The spec says the default is "tls-unique"
22 : * (RFC 5802, section 6.1. Default Channel Binding), but there are some
23 : * problems with that. Firstly, not all SSL libraries provide an API to
24 : * get the TLS Finished message, required to use "tls-unique". Secondly,
25 : * "tls-unique" is not specified for TLS v1.3, and as of this writing,
26 : * it's not clear if there will be a replacement. We could support both
27 : * "tls-server-end-point" and "tls-unique", but for our use case,
28 : * "tls-unique" doesn't really have any advantages. The main advantage
29 : * of "tls-unique" would be that it works even if the server doesn't
30 : * have a certificate, but PostgreSQL requires a server certificate
31 : * whenever SSL is used, anyway.
32 : *
33 : *
34 : * The password stored in pg_authid consists of the iteration count, salt,
35 : * StoredKey and ServerKey.
36 : *
37 : * SASLprep usage
38 : * --------------
39 : *
40 : * One notable difference to the SCRAM specification is that while the
41 : * specification dictates that the password is in UTF-8, and prohibits
42 : * certain characters, we are more lenient. If the password isn't a valid
43 : * UTF-8 string, or contains prohibited characters, the raw bytes are used
44 : * to calculate the hash instead, without SASLprep processing. This is
45 : * because PostgreSQL supports other encodings too, and the encoding being
46 : * used during authentication is undefined (client_encoding isn't set until
47 : * after authentication). In effect, we try to interpret the password as
48 : * UTF-8 and apply SASLprep processing, but if it looks invalid, we assume
49 : * that it's in some other encoding.
50 : *
51 : * In the worst case, we misinterpret a password that's in a different
52 : * encoding as being Unicode, because it happens to consists entirely of
53 : * valid UTF-8 bytes, and we apply Unicode normalization to it. As long
54 : * as we do that consistently, that will not lead to failed logins.
55 : * Fortunately, the UTF-8 byte sequences that are ignored by SASLprep
56 : * don't correspond to any commonly used characters in any of the other
57 : * supported encodings, so it should not lead to any significant loss in
58 : * entropy, even if the normalization is incorrectly applied to a
59 : * non-UTF-8 password.
60 : *
61 : * Error handling
62 : * --------------
63 : *
64 : * Don't reveal user information to an unauthenticated client. We don't
65 : * want an attacker to be able to probe whether a particular username is
66 : * valid. In SCRAM, the server has to read the salt and iteration count
67 : * from the user's stored secret, and send it to the client. To avoid
68 : * revealing whether a user exists, when the client tries to authenticate
69 : * with a username that doesn't exist, or doesn't have a valid SCRAM
70 : * secret in pg_authid, we create a fake salt and iteration count
71 : * on-the-fly, and proceed with the authentication with that. In the end,
72 : * we'll reject the attempt, as if an incorrect password was given. When
73 : * we are performing a "mock" authentication, the 'doomed' flag in
74 : * scram_state is set.
75 : *
76 : * In the error messages, avoid printing strings from the client, unless
77 : * you check that they are pure ASCII. We don't want an unauthenticated
78 : * attacker to be able to spam the logs with characters that are not valid
79 : * to the encoding being used, whatever that is. We cannot avoid that in
80 : * general, after logging in, but let's do what we can here.
81 : *
82 : *
83 : * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
84 : * Portions Copyright (c) 1994, Regents of the University of California
85 : *
86 : * src/backend/libpq/auth-scram.c
87 : *
88 : *-------------------------------------------------------------------------
89 : */
90 : #include "postgres.h"
91 :
92 : #include <unistd.h>
93 :
94 : #include "access/xlog.h"
95 : #include "catalog/pg_control.h"
96 : #include "common/base64.h"
97 : #include "common/hmac.h"
98 : #include "common/saslprep.h"
99 : #include "common/scram-common.h"
100 : #include "common/sha2.h"
101 : #include "libpq/crypt.h"
102 : #include "libpq/sasl.h"
103 : #include "libpq/scram.h"
104 :
105 : static void scram_get_mechanisms(Port *port, StringInfo buf);
106 : static void *scram_init(Port *port, const char *selected_mech,
107 : const char *shadow_pass);
108 : static int scram_exchange(void *opaq, const char *input, int inputlen,
109 : char **output, int *outputlen,
110 : const char **logdetail);
111 :
112 : /* Mechanism declaration */
113 : const pg_be_sasl_mech pg_be_scram_mech = {
114 : scram_get_mechanisms,
115 : scram_init,
116 : scram_exchange
117 : };
118 :
119 : /*
120 : * Status data for a SCRAM authentication exchange. This should be kept
121 : * internal to this file.
122 : */
123 : typedef enum
124 : {
125 : SCRAM_AUTH_INIT,
126 : SCRAM_AUTH_SALT_SENT,
127 : SCRAM_AUTH_FINISHED,
128 : } scram_state_enum;
129 :
130 : typedef struct
131 : {
132 : scram_state_enum state;
133 :
134 : const char *username; /* username from startup packet */
135 :
136 : Port *port;
137 : bool channel_binding_in_use;
138 :
139 : /* State data depending on the hash type */
140 : pg_cryptohash_type hash_type;
141 : int key_length;
142 :
143 : int iterations;
144 : char *salt; /* base64-encoded */
145 : uint8 StoredKey[SCRAM_MAX_KEY_LEN];
146 : uint8 ServerKey[SCRAM_MAX_KEY_LEN];
147 :
148 : /* Fields of the first message from client */
149 : char cbind_flag;
150 : char *client_first_message_bare;
151 : char *client_username;
152 : char *client_nonce;
153 :
154 : /* Fields from the last message from client */
155 : char *client_final_message_without_proof;
156 : char *client_final_nonce;
157 : char ClientProof[SCRAM_MAX_KEY_LEN];
158 :
159 : /* Fields generated in the server */
160 : char *server_first_message;
161 : char *server_nonce;
162 :
163 : /*
164 : * If something goes wrong during the authentication, or we are performing
165 : * a "mock" authentication (see comments at top of file), the 'doomed'
166 : * flag is set. A reason for the failure, for the server log, is put in
167 : * 'logdetail'.
168 : */
169 : bool doomed;
170 : char *logdetail;
171 : } scram_state;
172 :
173 : static void read_client_first_message(scram_state *state, const char *input);
174 : static void read_client_final_message(scram_state *state, const char *input);
175 : static char *build_server_first_message(scram_state *state);
176 : static char *build_server_final_message(scram_state *state);
177 : static bool verify_client_proof(scram_state *state);
178 : static bool verify_final_nonce(scram_state *state);
179 : static void mock_scram_secret(const char *username, pg_cryptohash_type *hash_type,
180 : int *iterations, int *key_length, char **salt,
181 : uint8 *stored_key, uint8 *server_key);
182 : static bool is_scram_printable(char *p);
183 : static char *sanitize_char(char c);
184 : static char *sanitize_str(const char *s);
185 : static char *scram_mock_salt(const char *username,
186 : pg_cryptohash_type hash_type,
187 : int key_length);
188 :
189 : /*
190 : * The number of iterations to use when generating new secrets.
191 : */
192 : int scram_sha_256_iterations = SCRAM_SHA_256_DEFAULT_ITERATIONS;
193 :
194 : /*
195 : * Get a list of SASL mechanisms that this module supports.
196 : *
197 : * For the convenience of building the FE/BE packet that lists the
198 : * mechanisms, the names are appended to the given StringInfo buffer,
199 : * separated by '\0' bytes.
200 : */
201 : static void
202 100 : scram_get_mechanisms(Port *port, StringInfo buf)
203 : {
204 : /*
205 : * Advertise the mechanisms in decreasing order of importance. So the
206 : * channel-binding variants go first, if they are supported. Channel
207 : * binding is only supported with SSL.
208 : */
209 : #ifdef USE_SSL
210 100 : if (port->ssl_in_use)
211 : {
212 12 : appendStringInfoString(buf, SCRAM_SHA_256_PLUS_NAME);
213 12 : appendStringInfoChar(buf, '\0');
214 : }
215 : #endif
216 100 : appendStringInfoString(buf, SCRAM_SHA_256_NAME);
217 100 : appendStringInfoChar(buf, '\0');
218 100 : }
219 :
220 : /*
221 : * Initialize a new SCRAM authentication exchange status tracker. This
222 : * needs to be called before doing any exchange. It will be filled later
223 : * after the beginning of the exchange with authentication information.
224 : *
225 : * 'selected_mech' identifies the SASL mechanism that the client selected.
226 : * It should be one of the mechanisms that we support, as returned by
227 : * scram_get_mechanisms().
228 : *
229 : * 'shadow_pass' is the role's stored secret, from pg_authid.rolpassword.
230 : * The username was provided by the client in the startup message, and is
231 : * available in port->user_name. If 'shadow_pass' is NULL, we still perform
232 : * an authentication exchange, but it will fail, as if an incorrect password
233 : * was given.
234 : */
235 : static void *
236 78 : scram_init(Port *port, const char *selected_mech, const char *shadow_pass)
237 : {
238 : scram_state *state;
239 : bool got_secret;
240 :
241 78 : state = (scram_state *) palloc0(sizeof(scram_state));
242 78 : state->port = port;
243 78 : state->state = SCRAM_AUTH_INIT;
244 :
245 : /*
246 : * Parse the selected mechanism.
247 : *
248 : * Note that if we don't support channel binding, or if we're not using
249 : * SSL at all, we would not have advertised the PLUS variant in the first
250 : * place. If the client nevertheless tries to select it, it's a protocol
251 : * violation like selecting any other SASL mechanism we don't support.
252 : */
253 : #ifdef USE_SSL
254 78 : if (strcmp(selected_mech, SCRAM_SHA_256_PLUS_NAME) == 0 && port->ssl_in_use)
255 8 : state->channel_binding_in_use = true;
256 : else
257 : #endif
258 70 : if (strcmp(selected_mech, SCRAM_SHA_256_NAME) == 0)
259 70 : state->channel_binding_in_use = false;
260 : else
261 0 : ereport(ERROR,
262 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
263 : errmsg("client selected an invalid SASL authentication mechanism")));
264 :
265 : /*
266 : * Parse the stored secret.
267 : */
268 78 : if (shadow_pass)
269 : {
270 78 : int password_type = get_password_type(shadow_pass);
271 :
272 78 : if (password_type == PASSWORD_TYPE_SCRAM_SHA_256)
273 : {
274 76 : if (parse_scram_secret(shadow_pass, &state->iterations,
275 : &state->hash_type, &state->key_length,
276 : &state->salt,
277 76 : state->StoredKey,
278 76 : state->ServerKey))
279 76 : got_secret = true;
280 : else
281 : {
282 : /*
283 : * The password looked like a SCRAM secret, but could not be
284 : * parsed.
285 : */
286 0 : ereport(LOG,
287 : (errmsg("invalid SCRAM secret for user \"%s\"",
288 : state->port->user_name)));
289 0 : got_secret = false;
290 : }
291 : }
292 : else
293 : {
294 : /*
295 : * The user doesn't have SCRAM secret. (You cannot do SCRAM
296 : * authentication with an MD5 hash.)
297 : */
298 4 : state->logdetail = psprintf(_("User \"%s\" does not have a valid SCRAM secret."),
299 2 : state->port->user_name);
300 2 : got_secret = false;
301 : }
302 : }
303 : else
304 : {
305 : /*
306 : * The caller requested us to perform a dummy authentication. This is
307 : * considered normal, since the caller requested it, so don't set log
308 : * detail.
309 : */
310 0 : got_secret = false;
311 : }
312 :
313 : /*
314 : * If the user did not have a valid SCRAM secret, we still go through the
315 : * motions with a mock one, and fail as if the client supplied an
316 : * incorrect password. This is to avoid revealing information to an
317 : * attacker.
318 : */
319 78 : if (!got_secret)
320 : {
321 2 : mock_scram_secret(state->port->user_name, &state->hash_type,
322 : &state->iterations, &state->key_length,
323 : &state->salt,
324 2 : state->StoredKey, state->ServerKey);
325 2 : state->doomed = true;
326 : }
327 :
328 78 : return state;
329 : }
330 :
331 : /*
332 : * Continue a SCRAM authentication exchange.
333 : *
334 : * 'input' is the SCRAM payload sent by the client. On the first call,
335 : * 'input' contains the "Initial Client Response" that the client sent as
336 : * part of the SASLInitialResponse message, or NULL if no Initial Client
337 : * Response was given. (The SASL specification distinguishes between an
338 : * empty response and non-existing one.) On subsequent calls, 'input'
339 : * cannot be NULL. For convenience in this function, the caller must
340 : * ensure that there is a null terminator at input[inputlen].
341 : *
342 : * The next message to send to client is saved in 'output', for a length
343 : * of 'outputlen'. In the case of an error, optionally store a palloc'd
344 : * string at *logdetail that will be sent to the postmaster log (but not
345 : * the client).
346 : */
347 : static int
348 156 : scram_exchange(void *opaq, const char *input, int inputlen,
349 : char **output, int *outputlen, const char **logdetail)
350 : {
351 156 : scram_state *state = (scram_state *) opaq;
352 : int result;
353 :
354 156 : *output = NULL;
355 :
356 : /*
357 : * If the client didn't include an "Initial Client Response" in the
358 : * SASLInitialResponse message, send an empty challenge, to which the
359 : * client will respond with the same data that usually comes in the
360 : * Initial Client Response.
361 : */
362 156 : if (input == NULL)
363 : {
364 : Assert(state->state == SCRAM_AUTH_INIT);
365 :
366 0 : *output = pstrdup("");
367 0 : *outputlen = 0;
368 0 : return PG_SASL_EXCHANGE_CONTINUE;
369 : }
370 :
371 : /*
372 : * Check that the input length agrees with the string length of the input.
373 : * We can ignore inputlen after this.
374 : */
375 156 : if (inputlen == 0)
376 0 : ereport(ERROR,
377 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
378 : errmsg("malformed SCRAM message"),
379 : errdetail("The message is empty.")));
380 156 : if (inputlen != strlen(input))
381 0 : ereport(ERROR,
382 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
383 : errmsg("malformed SCRAM message"),
384 : errdetail("Message length does not match input length.")));
385 :
386 156 : switch (state->state)
387 : {
388 78 : case SCRAM_AUTH_INIT:
389 :
390 : /*
391 : * Initialization phase. Receive the first message from client
392 : * and be sure that it parsed correctly. Then send the challenge
393 : * to the client.
394 : */
395 78 : read_client_first_message(state, input);
396 :
397 : /* prepare message to send challenge */
398 78 : *output = build_server_first_message(state);
399 :
400 78 : state->state = SCRAM_AUTH_SALT_SENT;
401 78 : result = PG_SASL_EXCHANGE_CONTINUE;
402 78 : break;
403 :
404 78 : case SCRAM_AUTH_SALT_SENT:
405 :
406 : /*
407 : * Final phase for the server. Receive the response to the
408 : * challenge previously sent, verify, and let the client know that
409 : * everything went well (or not).
410 : */
411 78 : read_client_final_message(state, input);
412 :
413 78 : if (!verify_final_nonce(state))
414 0 : ereport(ERROR,
415 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
416 : errmsg("invalid SCRAM response"),
417 : errdetail("Nonce does not match.")));
418 :
419 : /*
420 : * Now check the final nonce and the client proof.
421 : *
422 : * If we performed a "mock" authentication that we knew would fail
423 : * from the get go, this is where we fail.
424 : *
425 : * The SCRAM specification includes an error code,
426 : * "invalid-proof", for authentication failure, but it also allows
427 : * erroring out in an application-specific way. We choose to do
428 : * the latter, so that the error message for invalid password is
429 : * the same for all authentication methods. The caller will call
430 : * ereport(), when we return PG_SASL_EXCHANGE_FAILURE with no
431 : * output.
432 : *
433 : * NB: the order of these checks is intentional. We calculate the
434 : * client proof even in a mock authentication, even though it's
435 : * bound to fail, to thwart timing attacks to determine if a role
436 : * with the given name exists or not.
437 : */
438 78 : if (!verify_client_proof(state) || state->doomed)
439 : {
440 12 : result = PG_SASL_EXCHANGE_FAILURE;
441 12 : break;
442 : }
443 :
444 : /* Build final message for client */
445 66 : *output = build_server_final_message(state);
446 :
447 : /* Success! */
448 66 : result = PG_SASL_EXCHANGE_SUCCESS;
449 66 : state->state = SCRAM_AUTH_FINISHED;
450 66 : break;
451 :
452 0 : default:
453 0 : elog(ERROR, "invalid SCRAM exchange state");
454 : result = PG_SASL_EXCHANGE_FAILURE;
455 : }
456 :
457 156 : if (result == PG_SASL_EXCHANGE_FAILURE && state->logdetail && logdetail)
458 2 : *logdetail = state->logdetail;
459 :
460 156 : if (*output)
461 144 : *outputlen = strlen(*output);
462 :
463 156 : return result;
464 : }
465 :
466 : /*
467 : * Construct a SCRAM secret, for storing in pg_authid.rolpassword.
468 : *
469 : * The result is palloc'd, so caller is responsible for freeing it.
470 : */
471 : char *
472 96 : pg_be_scram_build_secret(const char *password)
473 : {
474 : char *prep_password;
475 : pg_saslprep_rc rc;
476 : char saltbuf[SCRAM_DEFAULT_SALT_LEN];
477 : char *result;
478 96 : const char *errstr = NULL;
479 :
480 : /*
481 : * Normalize the password with SASLprep. If that doesn't work, because
482 : * the password isn't valid UTF-8 or contains prohibited characters, just
483 : * proceed with the original password. (See comments at top of file.)
484 : */
485 96 : rc = pg_saslprep(password, &prep_password);
486 96 : if (rc == SASLPREP_SUCCESS)
487 94 : password = (const char *) prep_password;
488 :
489 : /* Generate random salt */
490 96 : if (!pg_strong_random(saltbuf, SCRAM_DEFAULT_SALT_LEN))
491 0 : ereport(ERROR,
492 : (errcode(ERRCODE_INTERNAL_ERROR),
493 : errmsg("could not generate random salt")));
494 :
495 96 : result = scram_build_secret(PG_SHA256, SCRAM_SHA_256_KEY_LEN,
496 : saltbuf, SCRAM_DEFAULT_SALT_LEN,
497 : scram_sha_256_iterations, password,
498 : &errstr);
499 :
500 96 : if (prep_password)
501 94 : pfree(prep_password);
502 :
503 96 : return result;
504 : }
505 :
506 : /*
507 : * Verify a plaintext password against a SCRAM secret. This is used when
508 : * performing plaintext password authentication for a user that has a SCRAM
509 : * secret stored in pg_authid.
510 : */
511 : bool
512 38 : scram_verify_plain_password(const char *username, const char *password,
513 : const char *secret)
514 : {
515 : char *encoded_salt;
516 : char *salt;
517 : int saltlen;
518 : int iterations;
519 38 : int key_length = 0;
520 : pg_cryptohash_type hash_type;
521 : uint8 salted_password[SCRAM_MAX_KEY_LEN];
522 : uint8 stored_key[SCRAM_MAX_KEY_LEN];
523 : uint8 server_key[SCRAM_MAX_KEY_LEN];
524 : uint8 computed_key[SCRAM_MAX_KEY_LEN];
525 : char *prep_password;
526 : pg_saslprep_rc rc;
527 38 : const char *errstr = NULL;
528 :
529 38 : if (!parse_scram_secret(secret, &iterations, &hash_type, &key_length,
530 : &encoded_salt, stored_key, server_key))
531 : {
532 : /*
533 : * The password looked like a SCRAM secret, but could not be parsed.
534 : */
535 0 : ereport(LOG,
536 : (errmsg("invalid SCRAM secret for user \"%s\"", username)));
537 0 : return false;
538 : }
539 :
540 38 : saltlen = pg_b64_dec_len(strlen(encoded_salt));
541 38 : salt = palloc(saltlen);
542 38 : saltlen = pg_b64_decode(encoded_salt, strlen(encoded_salt), salt,
543 : saltlen);
544 38 : if (saltlen < 0)
545 : {
546 0 : ereport(LOG,
547 : (errmsg("invalid SCRAM secret for user \"%s\"", username)));
548 0 : return false;
549 : }
550 :
551 : /* Normalize the password */
552 38 : rc = pg_saslprep(password, &prep_password);
553 38 : if (rc == SASLPREP_SUCCESS)
554 38 : password = prep_password;
555 :
556 : /* Compute Server Key based on the user-supplied plaintext password */
557 38 : if (scram_SaltedPassword(password, hash_type, key_length,
558 : salt, saltlen, iterations,
559 38 : salted_password, &errstr) < 0 ||
560 38 : scram_ServerKey(salted_password, hash_type, key_length,
561 : computed_key, &errstr) < 0)
562 : {
563 0 : elog(ERROR, "could not compute server key: %s", errstr);
564 : }
565 :
566 38 : if (prep_password)
567 38 : pfree(prep_password);
568 :
569 : /*
570 : * Compare the secret's Server Key with the one computed from the
571 : * user-supplied password.
572 : */
573 38 : return memcmp(computed_key, server_key, key_length) == 0;
574 : }
575 :
576 :
577 : /*
578 : * Parse and validate format of given SCRAM secret.
579 : *
580 : * On success, the iteration count, salt, stored key, and server key are
581 : * extracted from the secret, and returned to the caller. For 'stored_key'
582 : * and 'server_key', the caller must pass pre-allocated buffers of size
583 : * SCRAM_MAX_KEY_LEN. Salt is returned as a base64-encoded, null-terminated
584 : * string. The buffer for the salt is palloc'd by this function.
585 : *
586 : * Returns true if the SCRAM secret has been parsed, and false otherwise.
587 : */
588 : bool
589 584 : parse_scram_secret(const char *secret, int *iterations,
590 : pg_cryptohash_type *hash_type, int *key_length,
591 : char **salt, uint8 *stored_key, uint8 *server_key)
592 : {
593 : char *v;
594 : char *p;
595 : char *scheme_str;
596 : char *salt_str;
597 : char *iterations_str;
598 : char *storedkey_str;
599 : char *serverkey_str;
600 : int decoded_len;
601 : char *decoded_salt_buf;
602 : char *decoded_stored_buf;
603 : char *decoded_server_buf;
604 :
605 : /*
606 : * The secret is of form:
607 : *
608 : * SCRAM-SHA-256$<iterations>:<salt>$<storedkey>:<serverkey>
609 : */
610 584 : v = pstrdup(secret);
611 584 : if ((scheme_str = strtok(v, "$")) == NULL)
612 0 : goto invalid_secret;
613 584 : if ((iterations_str = strtok(NULL, ":")) == NULL)
614 208 : goto invalid_secret;
615 376 : if ((salt_str = strtok(NULL, "$")) == NULL)
616 12 : goto invalid_secret;
617 364 : if ((storedkey_str = strtok(NULL, ":")) == NULL)
618 0 : goto invalid_secret;
619 364 : if ((serverkey_str = strtok(NULL, "")) == NULL)
620 0 : goto invalid_secret;
621 :
622 : /* Parse the fields */
623 364 : if (strcmp(scheme_str, "SCRAM-SHA-256") != 0)
624 0 : goto invalid_secret;
625 364 : *hash_type = PG_SHA256;
626 364 : *key_length = SCRAM_SHA_256_KEY_LEN;
627 :
628 364 : errno = 0;
629 364 : *iterations = strtol(iterations_str, &p, 10);
630 364 : if (*p || errno != 0)
631 0 : goto invalid_secret;
632 :
633 : /*
634 : * Verify that the salt is in Base64-encoded format, by decoding it,
635 : * although we return the encoded version to the caller.
636 : */
637 364 : decoded_len = pg_b64_dec_len(strlen(salt_str));
638 364 : decoded_salt_buf = palloc(decoded_len);
639 364 : decoded_len = pg_b64_decode(salt_str, strlen(salt_str),
640 : decoded_salt_buf, decoded_len);
641 364 : if (decoded_len < 0)
642 0 : goto invalid_secret;
643 364 : *salt = pstrdup(salt_str);
644 :
645 : /*
646 : * Decode StoredKey and ServerKey.
647 : */
648 364 : decoded_len = pg_b64_dec_len(strlen(storedkey_str));
649 364 : decoded_stored_buf = palloc(decoded_len);
650 364 : decoded_len = pg_b64_decode(storedkey_str, strlen(storedkey_str),
651 : decoded_stored_buf, decoded_len);
652 364 : if (decoded_len != *key_length)
653 12 : goto invalid_secret;
654 352 : memcpy(stored_key, decoded_stored_buf, *key_length);
655 :
656 352 : decoded_len = pg_b64_dec_len(strlen(serverkey_str));
657 352 : decoded_server_buf = palloc(decoded_len);
658 352 : decoded_len = pg_b64_decode(serverkey_str, strlen(serverkey_str),
659 : decoded_server_buf, decoded_len);
660 352 : if (decoded_len != *key_length)
661 12 : goto invalid_secret;
662 340 : memcpy(server_key, decoded_server_buf, *key_length);
663 :
664 340 : return true;
665 :
666 244 : invalid_secret:
667 244 : *salt = NULL;
668 244 : return false;
669 : }
670 :
671 : /*
672 : * Generate plausible SCRAM secret parameters for mock authentication.
673 : *
674 : * In a normal authentication, these are extracted from the secret
675 : * stored in the server. This function generates values that look
676 : * realistic, for when there is no stored secret, using SCRAM-SHA-256.
677 : *
678 : * Like in parse_scram_secret(), for 'stored_key' and 'server_key', the
679 : * caller must pass pre-allocated buffers of size SCRAM_MAX_KEY_LEN, and
680 : * the buffer for the salt is palloc'd by this function.
681 : */
682 : static void
683 2 : mock_scram_secret(const char *username, pg_cryptohash_type *hash_type,
684 : int *iterations, int *key_length, char **salt,
685 : uint8 *stored_key, uint8 *server_key)
686 : {
687 : char *raw_salt;
688 : char *encoded_salt;
689 : int encoded_len;
690 :
691 : /* Enforce the use of SHA-256, which would be realistic enough */
692 2 : *hash_type = PG_SHA256;
693 2 : *key_length = SCRAM_SHA_256_KEY_LEN;
694 :
695 : /*
696 : * Generate deterministic salt.
697 : *
698 : * Note that we cannot reveal any information to an attacker here so the
699 : * error messages need to remain generic. This should never fail anyway
700 : * as the salt generated for mock authentication uses the cluster's nonce
701 : * value.
702 : */
703 2 : raw_salt = scram_mock_salt(username, *hash_type, *key_length);
704 2 : if (raw_salt == NULL)
705 0 : elog(ERROR, "could not encode salt");
706 :
707 2 : encoded_len = pg_b64_enc_len(SCRAM_DEFAULT_SALT_LEN);
708 : /* don't forget the zero-terminator */
709 2 : encoded_salt = (char *) palloc(encoded_len + 1);
710 2 : encoded_len = pg_b64_encode(raw_salt, SCRAM_DEFAULT_SALT_LEN, encoded_salt,
711 : encoded_len);
712 :
713 2 : if (encoded_len < 0)
714 0 : elog(ERROR, "could not encode salt");
715 2 : encoded_salt[encoded_len] = '\0';
716 :
717 2 : *salt = encoded_salt;
718 2 : *iterations = SCRAM_SHA_256_DEFAULT_ITERATIONS;
719 :
720 : /* StoredKey and ServerKey are not used in a doomed authentication */
721 2 : memset(stored_key, 0, SCRAM_MAX_KEY_LEN);
722 2 : memset(server_key, 0, SCRAM_MAX_KEY_LEN);
723 2 : }
724 :
725 : /*
726 : * Read the value in a given SCRAM exchange message for given attribute.
727 : */
728 : static char *
729 320 : read_attr_value(char **input, char attr)
730 : {
731 320 : char *begin = *input;
732 : char *end;
733 :
734 320 : if (*begin != attr)
735 0 : ereport(ERROR,
736 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
737 : errmsg("malformed SCRAM message"),
738 : errdetail("Expected attribute \"%c\" but found \"%s\".",
739 : attr, sanitize_char(*begin))));
740 320 : begin++;
741 :
742 320 : if (*begin != '=')
743 0 : ereport(ERROR,
744 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
745 : errmsg("malformed SCRAM message"),
746 : errdetail("Expected character \"=\" for attribute \"%c\".", attr)));
747 320 : begin++;
748 :
749 320 : end = begin;
750 6984 : while (*end && *end != ',')
751 6664 : end++;
752 :
753 320 : if (*end)
754 : {
755 242 : *end = '\0';
756 242 : *input = end + 1;
757 : }
758 : else
759 78 : *input = end;
760 :
761 320 : return begin;
762 : }
763 :
764 : static bool
765 78 : is_scram_printable(char *p)
766 : {
767 : /*------
768 : * Printable characters, as defined by SCRAM spec: (RFC 5802)
769 : *
770 : * printable = %x21-2B / %x2D-7E
771 : * ;; Printable ASCII except ",".
772 : * ;; Note that any "printable" is also
773 : * ;; a valid "value".
774 : *------
775 : */
776 1950 : for (; *p; p++)
777 : {
778 1872 : if (*p < 0x21 || *p > 0x7E || *p == 0x2C /* comma */ )
779 0 : return false;
780 : }
781 78 : return true;
782 : }
783 :
784 : /*
785 : * Convert an arbitrary byte to printable form. For error messages.
786 : *
787 : * If it's a printable ASCII character, print it as a single character.
788 : * otherwise, print it in hex.
789 : *
790 : * The returned pointer points to a static buffer.
791 : */
792 : static char *
793 0 : sanitize_char(char c)
794 : {
795 : static char buf[5];
796 :
797 0 : if (c >= 0x21 && c <= 0x7E)
798 0 : snprintf(buf, sizeof(buf), "'%c'", c);
799 : else
800 0 : snprintf(buf, sizeof(buf), "0x%02x", (unsigned char) c);
801 0 : return buf;
802 : }
803 :
804 : /*
805 : * Convert an arbitrary string to printable form, for error messages.
806 : *
807 : * Anything that's not a printable ASCII character is replaced with
808 : * '?', and the string is truncated at 30 characters.
809 : *
810 : * The returned pointer points to a static buffer.
811 : */
812 : static char *
813 0 : sanitize_str(const char *s)
814 : {
815 : static char buf[30 + 1];
816 : int i;
817 :
818 0 : for (i = 0; i < sizeof(buf) - 1; i++)
819 : {
820 0 : char c = s[i];
821 :
822 0 : if (c == '\0')
823 0 : break;
824 :
825 0 : if (c >= 0x21 && c <= 0x7E)
826 0 : buf[i] = c;
827 : else
828 0 : buf[i] = '?';
829 : }
830 0 : buf[i] = '\0';
831 0 : return buf;
832 : }
833 :
834 : /*
835 : * Read the next attribute and value in a SCRAM exchange message.
836 : *
837 : * The attribute character is set in *attr_p, the attribute value is the
838 : * return value.
839 : */
840 : static char *
841 78 : read_any_attr(char **input, char *attr_p)
842 : {
843 78 : char *begin = *input;
844 : char *end;
845 78 : char attr = *begin;
846 :
847 78 : if (attr == '\0')
848 0 : ereport(ERROR,
849 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
850 : errmsg("malformed SCRAM message"),
851 : errdetail("Attribute expected, but found end of string.")));
852 :
853 : /*------
854 : * attr-val = ALPHA "=" value
855 : * ;; Generic syntax of any attribute sent
856 : * ;; by server or client
857 : *------
858 : */
859 78 : if (!((attr >= 'A' && attr <= 'Z') ||
860 78 : (attr >= 'a' && attr <= 'z')))
861 0 : ereport(ERROR,
862 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
863 : errmsg("malformed SCRAM message"),
864 : errdetail("Attribute expected, but found invalid character \"%s\".",
865 : sanitize_char(attr))));
866 78 : if (attr_p)
867 78 : *attr_p = attr;
868 78 : begin++;
869 :
870 78 : if (*begin != '=')
871 0 : ereport(ERROR,
872 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
873 : errmsg("malformed SCRAM message"),
874 : errdetail("Expected character \"=\" for attribute \"%c\".", attr)));
875 78 : begin++;
876 :
877 78 : end = begin;
878 3510 : while (*end && *end != ',')
879 3432 : end++;
880 :
881 78 : if (*end)
882 : {
883 0 : *end = '\0';
884 0 : *input = end + 1;
885 : }
886 : else
887 78 : *input = end;
888 :
889 78 : return begin;
890 : }
891 :
892 : /*
893 : * Read and parse the first message from client in the context of a SCRAM
894 : * authentication exchange message.
895 : *
896 : * At this stage, any errors will be reported directly with ereport(ERROR).
897 : */
898 : static void
899 78 : read_client_first_message(scram_state *state, const char *input)
900 : {
901 78 : char *p = pstrdup(input);
902 : char *channel_binding_type;
903 :
904 :
905 : /*------
906 : * The syntax for the client-first-message is: (RFC 5802)
907 : *
908 : * saslname = 1*(value-safe-char / "=2C" / "=3D")
909 : * ;; Conforms to <value>.
910 : *
911 : * authzid = "a=" saslname
912 : * ;; Protocol specific.
913 : *
914 : * cb-name = 1*(ALPHA / DIGIT / "." / "-")
915 : * ;; See RFC 5056, Section 7.
916 : * ;; E.g., "tls-server-end-point" or
917 : * ;; "tls-unique".
918 : *
919 : * gs2-cbind-flag = ("p=" cb-name) / "n" / "y"
920 : * ;; "n" -> client doesn't support channel binding.
921 : * ;; "y" -> client does support channel binding
922 : * ;; but thinks the server does not.
923 : * ;; "p" -> client requires channel binding.
924 : * ;; The selected channel binding follows "p=".
925 : *
926 : * gs2-header = gs2-cbind-flag "," [ authzid ] ","
927 : * ;; GS2 header for SCRAM
928 : * ;; (the actual GS2 header includes an optional
929 : * ;; flag to indicate that the GSS mechanism is not
930 : * ;; "standard", but since SCRAM is "standard", we
931 : * ;; don't include that flag).
932 : *
933 : * username = "n=" saslname
934 : * ;; Usernames are prepared using SASLprep.
935 : *
936 : * reserved-mext = "m=" 1*(value-char)
937 : * ;; Reserved for signaling mandatory extensions.
938 : * ;; The exact syntax will be defined in
939 : * ;; the future.
940 : *
941 : * nonce = "r=" c-nonce [s-nonce]
942 : * ;; Second part provided by server.
943 : *
944 : * c-nonce = printable
945 : *
946 : * client-first-message-bare =
947 : * [reserved-mext ","]
948 : * username "," nonce ["," extensions]
949 : *
950 : * client-first-message =
951 : * gs2-header client-first-message-bare
952 : *
953 : * For example:
954 : * n,,n=user,r=fyko+d2lbbFgONRv9qkxdawL
955 : *
956 : * The "n,," in the beginning means that the client doesn't support
957 : * channel binding, and no authzid is given. "n=user" is the username.
958 : * However, in PostgreSQL the username is sent in the startup packet, and
959 : * the username in the SCRAM exchange is ignored. libpq always sends it
960 : * as an empty string. The last part, "r=fyko+d2lbbFgONRv9qkxdawL" is
961 : * the client nonce.
962 : *------
963 : */
964 :
965 : /*
966 : * Read gs2-cbind-flag. (For details see also RFC 5802 Section 6 "Channel
967 : * Binding".)
968 : */
969 78 : state->cbind_flag = *p;
970 78 : switch (*p)
971 : {
972 70 : case 'n':
973 :
974 : /*
975 : * The client does not support channel binding or has simply
976 : * decided to not use it. In that case just let it go.
977 : */
978 70 : if (state->channel_binding_in_use)
979 0 : ereport(ERROR,
980 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
981 : errmsg("malformed SCRAM message"),
982 : errdetail("The client selected SCRAM-SHA-256-PLUS, but the SCRAM message does not include channel binding data.")));
983 :
984 70 : p++;
985 70 : if (*p != ',')
986 0 : ereport(ERROR,
987 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
988 : errmsg("malformed SCRAM message"),
989 : errdetail("Comma expected, but found character \"%s\".",
990 : sanitize_char(*p))));
991 70 : p++;
992 70 : break;
993 0 : case 'y':
994 :
995 : /*
996 : * The client supports channel binding and thinks that the server
997 : * does not. In this case, the server must fail authentication if
998 : * it supports channel binding.
999 : */
1000 0 : if (state->channel_binding_in_use)
1001 0 : ereport(ERROR,
1002 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1003 : errmsg("malformed SCRAM message"),
1004 : errdetail("The client selected SCRAM-SHA-256-PLUS, but the SCRAM message does not include channel binding data.")));
1005 :
1006 : #ifdef USE_SSL
1007 0 : if (state->port->ssl_in_use)
1008 0 : ereport(ERROR,
1009 : (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
1010 : errmsg("SCRAM channel binding negotiation error"),
1011 : errdetail("The client supports SCRAM channel binding but thinks the server does not. "
1012 : "However, this server does support channel binding.")));
1013 : #endif
1014 0 : p++;
1015 0 : if (*p != ',')
1016 0 : ereport(ERROR,
1017 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1018 : errmsg("malformed SCRAM message"),
1019 : errdetail("Comma expected, but found character \"%s\".",
1020 : sanitize_char(*p))));
1021 0 : p++;
1022 0 : break;
1023 8 : case 'p':
1024 :
1025 : /*
1026 : * The client requires channel binding. Channel binding type
1027 : * follows, e.g., "p=tls-server-end-point".
1028 : */
1029 8 : if (!state->channel_binding_in_use)
1030 0 : ereport(ERROR,
1031 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1032 : errmsg("malformed SCRAM message"),
1033 : errdetail("The client selected SCRAM-SHA-256 without channel binding, but the SCRAM message includes channel binding data.")));
1034 :
1035 8 : channel_binding_type = read_attr_value(&p, 'p');
1036 :
1037 : /*
1038 : * The only channel binding type we support is
1039 : * tls-server-end-point.
1040 : */
1041 8 : if (strcmp(channel_binding_type, "tls-server-end-point") != 0)
1042 0 : ereport(ERROR,
1043 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1044 : errmsg("unsupported SCRAM channel-binding type \"%s\"",
1045 : sanitize_str(channel_binding_type))));
1046 8 : break;
1047 0 : default:
1048 0 : ereport(ERROR,
1049 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1050 : errmsg("malformed SCRAM message"),
1051 : errdetail("Unexpected channel-binding flag \"%s\".",
1052 : sanitize_char(*p))));
1053 : }
1054 :
1055 : /*
1056 : * Forbid optional authzid (authorization identity). We don't support it.
1057 : */
1058 78 : if (*p == 'a')
1059 0 : ereport(ERROR,
1060 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1061 : errmsg("client uses authorization identity, but it is not supported")));
1062 78 : if (*p != ',')
1063 0 : ereport(ERROR,
1064 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1065 : errmsg("malformed SCRAM message"),
1066 : errdetail("Unexpected attribute \"%s\" in client-first-message.",
1067 : sanitize_char(*p))));
1068 78 : p++;
1069 :
1070 78 : state->client_first_message_bare = pstrdup(p);
1071 :
1072 : /*
1073 : * Any mandatory extensions would go here. We don't support any.
1074 : *
1075 : * RFC 5802 specifies error code "e=extensions-not-supported" for this,
1076 : * but it can only be sent in the server-final message. We prefer to fail
1077 : * immediately (which the RFC also allows).
1078 : */
1079 78 : if (*p == 'm')
1080 0 : ereport(ERROR,
1081 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1082 : errmsg("client requires an unsupported SCRAM extension")));
1083 :
1084 : /*
1085 : * Read username. Note: this is ignored. We use the username from the
1086 : * startup message instead, still it is kept around if provided as it
1087 : * proves to be useful for debugging purposes.
1088 : */
1089 78 : state->client_username = read_attr_value(&p, 'n');
1090 :
1091 : /* read nonce and check that it is made of only printable characters */
1092 78 : state->client_nonce = read_attr_value(&p, 'r');
1093 78 : if (!is_scram_printable(state->client_nonce))
1094 0 : ereport(ERROR,
1095 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1096 : errmsg("non-printable characters in SCRAM nonce")));
1097 :
1098 : /*
1099 : * There can be any number of optional extensions after this. We don't
1100 : * support any extensions, so ignore them.
1101 : */
1102 78 : while (*p != '\0')
1103 0 : read_any_attr(&p, NULL);
1104 :
1105 : /* success! */
1106 78 : }
1107 :
1108 : /*
1109 : * Verify the final nonce contained in the last message received from
1110 : * client in an exchange.
1111 : */
1112 : static bool
1113 78 : verify_final_nonce(scram_state *state)
1114 : {
1115 78 : int client_nonce_len = strlen(state->client_nonce);
1116 78 : int server_nonce_len = strlen(state->server_nonce);
1117 78 : int final_nonce_len = strlen(state->client_final_nonce);
1118 :
1119 78 : if (final_nonce_len != client_nonce_len + server_nonce_len)
1120 0 : return false;
1121 78 : if (memcmp(state->client_final_nonce, state->client_nonce, client_nonce_len) != 0)
1122 0 : return false;
1123 78 : if (memcmp(state->client_final_nonce + client_nonce_len, state->server_nonce, server_nonce_len) != 0)
1124 0 : return false;
1125 :
1126 78 : return true;
1127 : }
1128 :
1129 : /*
1130 : * Verify the client proof contained in the last message received from
1131 : * client in an exchange. Returns true if the verification is a success,
1132 : * or false for a failure.
1133 : */
1134 : static bool
1135 78 : verify_client_proof(scram_state *state)
1136 : {
1137 : uint8 ClientSignature[SCRAM_MAX_KEY_LEN];
1138 : uint8 ClientKey[SCRAM_MAX_KEY_LEN];
1139 : uint8 client_StoredKey[SCRAM_MAX_KEY_LEN];
1140 78 : pg_hmac_ctx *ctx = pg_hmac_create(state->hash_type);
1141 : int i;
1142 78 : const char *errstr = NULL;
1143 :
1144 : /*
1145 : * Calculate ClientSignature. Note that we don't log directly a failure
1146 : * here even when processing the calculations as this could involve a mock
1147 : * authentication.
1148 : */
1149 156 : if (pg_hmac_init(ctx, state->StoredKey, state->key_length) < 0 ||
1150 78 : pg_hmac_update(ctx,
1151 78 : (uint8 *) state->client_first_message_bare,
1152 156 : strlen(state->client_first_message_bare)) < 0 ||
1153 156 : pg_hmac_update(ctx, (uint8 *) ",", 1) < 0 ||
1154 78 : pg_hmac_update(ctx,
1155 78 : (uint8 *) state->server_first_message,
1156 156 : strlen(state->server_first_message)) < 0 ||
1157 156 : pg_hmac_update(ctx, (uint8 *) ",", 1) < 0 ||
1158 78 : pg_hmac_update(ctx,
1159 78 : (uint8 *) state->client_final_message_without_proof,
1160 156 : strlen(state->client_final_message_without_proof)) < 0 ||
1161 78 : pg_hmac_final(ctx, ClientSignature, state->key_length) < 0)
1162 : {
1163 0 : elog(ERROR, "could not calculate client signature: %s",
1164 : pg_hmac_error(ctx));
1165 : }
1166 :
1167 78 : pg_hmac_free(ctx);
1168 :
1169 : /* Extract the ClientKey that the client calculated from the proof */
1170 2574 : for (i = 0; i < state->key_length; i++)
1171 2496 : ClientKey[i] = state->ClientProof[i] ^ ClientSignature[i];
1172 :
1173 : /* Hash it one more time, and compare with StoredKey */
1174 78 : if (scram_H(ClientKey, state->hash_type, state->key_length,
1175 : client_StoredKey, &errstr) < 0)
1176 0 : elog(ERROR, "could not hash stored key: %s", errstr);
1177 :
1178 78 : if (memcmp(client_StoredKey, state->StoredKey, state->key_length) != 0)
1179 12 : return false;
1180 :
1181 66 : return true;
1182 : }
1183 :
1184 : /*
1185 : * Build the first server-side message sent to the client in a SCRAM
1186 : * communication exchange.
1187 : */
1188 : static char *
1189 78 : build_server_first_message(scram_state *state)
1190 : {
1191 : /*------
1192 : * The syntax for the server-first-message is: (RFC 5802)
1193 : *
1194 : * server-first-message =
1195 : * [reserved-mext ","] nonce "," salt ","
1196 : * iteration-count ["," extensions]
1197 : *
1198 : * nonce = "r=" c-nonce [s-nonce]
1199 : * ;; Second part provided by server.
1200 : *
1201 : * c-nonce = printable
1202 : *
1203 : * s-nonce = printable
1204 : *
1205 : * salt = "s=" base64
1206 : *
1207 : * iteration-count = "i=" posit-number
1208 : * ;; A positive number.
1209 : *
1210 : * Example:
1211 : *
1212 : * r=fyko+d2lbbFgONRv9qkxdawL3rfcNHYJY1ZVvWVs7j,s=QSXCR+Q6sek8bf92,i=4096
1213 : *------
1214 : */
1215 :
1216 : /*
1217 : * Per the spec, the nonce may consist of any printable ASCII characters.
1218 : * For convenience, however, we don't use the whole range available,
1219 : * rather, we generate some random bytes, and base64 encode them.
1220 : */
1221 : char raw_nonce[SCRAM_RAW_NONCE_LEN];
1222 : int encoded_len;
1223 :
1224 78 : if (!pg_strong_random(raw_nonce, SCRAM_RAW_NONCE_LEN))
1225 0 : ereport(ERROR,
1226 : (errcode(ERRCODE_INTERNAL_ERROR),
1227 : errmsg("could not generate random nonce")));
1228 :
1229 78 : encoded_len = pg_b64_enc_len(SCRAM_RAW_NONCE_LEN);
1230 : /* don't forget the zero-terminator */
1231 78 : state->server_nonce = palloc(encoded_len + 1);
1232 78 : encoded_len = pg_b64_encode(raw_nonce, SCRAM_RAW_NONCE_LEN,
1233 : state->server_nonce, encoded_len);
1234 78 : if (encoded_len < 0)
1235 0 : ereport(ERROR,
1236 : (errcode(ERRCODE_INTERNAL_ERROR),
1237 : errmsg("could not encode random nonce")));
1238 78 : state->server_nonce[encoded_len] = '\0';
1239 :
1240 78 : state->server_first_message =
1241 78 : psprintf("r=%s%s,s=%s,i=%d",
1242 : state->client_nonce, state->server_nonce,
1243 : state->salt, state->iterations);
1244 :
1245 78 : return pstrdup(state->server_first_message);
1246 : }
1247 :
1248 :
1249 : /*
1250 : * Read and parse the final message received from client.
1251 : */
1252 : static void
1253 78 : read_client_final_message(scram_state *state, const char *input)
1254 : {
1255 : char attr;
1256 : char *channel_binding;
1257 : char *value;
1258 : char *begin,
1259 : *proof;
1260 : char *p;
1261 : char *client_proof;
1262 : int client_proof_len;
1263 :
1264 78 : begin = p = pstrdup(input);
1265 :
1266 : /*------
1267 : * The syntax for the server-first-message is: (RFC 5802)
1268 : *
1269 : * gs2-header = gs2-cbind-flag "," [ authzid ] ","
1270 : * ;; GS2 header for SCRAM
1271 : * ;; (the actual GS2 header includes an optional
1272 : * ;; flag to indicate that the GSS mechanism is not
1273 : * ;; "standard", but since SCRAM is "standard", we
1274 : * ;; don't include that flag).
1275 : *
1276 : * cbind-input = gs2-header [ cbind-data ]
1277 : * ;; cbind-data MUST be present for
1278 : * ;; gs2-cbind-flag of "p" and MUST be absent
1279 : * ;; for "y" or "n".
1280 : *
1281 : * channel-binding = "c=" base64
1282 : * ;; base64 encoding of cbind-input.
1283 : *
1284 : * proof = "p=" base64
1285 : *
1286 : * client-final-message-without-proof =
1287 : * channel-binding "," nonce [","
1288 : * extensions]
1289 : *
1290 : * client-final-message =
1291 : * client-final-message-without-proof "," proof
1292 : *------
1293 : */
1294 :
1295 : /*
1296 : * Read channel binding. This repeats the channel-binding flags and is
1297 : * then followed by the actual binding data depending on the type.
1298 : */
1299 78 : channel_binding = read_attr_value(&p, 'c');
1300 78 : if (state->channel_binding_in_use)
1301 : {
1302 : #ifdef USE_SSL
1303 8 : const char *cbind_data = NULL;
1304 8 : size_t cbind_data_len = 0;
1305 : size_t cbind_header_len;
1306 : char *cbind_input;
1307 : size_t cbind_input_len;
1308 : char *b64_message;
1309 : int b64_message_len;
1310 :
1311 : Assert(state->cbind_flag == 'p');
1312 :
1313 : /* Fetch hash data of server's SSL certificate */
1314 8 : cbind_data = be_tls_get_certificate_hash(state->port,
1315 : &cbind_data_len);
1316 :
1317 : /* should not happen */
1318 8 : if (cbind_data == NULL || cbind_data_len == 0)
1319 0 : elog(ERROR, "could not get server certificate hash");
1320 :
1321 8 : cbind_header_len = strlen("p=tls-server-end-point,,"); /* p=type,, */
1322 8 : cbind_input_len = cbind_header_len + cbind_data_len;
1323 8 : cbind_input = palloc(cbind_input_len);
1324 8 : snprintf(cbind_input, cbind_input_len, "p=tls-server-end-point,,");
1325 8 : memcpy(cbind_input + cbind_header_len, cbind_data, cbind_data_len);
1326 :
1327 8 : b64_message_len = pg_b64_enc_len(cbind_input_len);
1328 : /* don't forget the zero-terminator */
1329 8 : b64_message = palloc(b64_message_len + 1);
1330 8 : b64_message_len = pg_b64_encode(cbind_input, cbind_input_len,
1331 : b64_message, b64_message_len);
1332 8 : if (b64_message_len < 0)
1333 0 : elog(ERROR, "could not encode channel binding data");
1334 8 : b64_message[b64_message_len] = '\0';
1335 :
1336 : /*
1337 : * Compare the value sent by the client with the value expected by the
1338 : * server.
1339 : */
1340 8 : if (strcmp(channel_binding, b64_message) != 0)
1341 0 : ereport(ERROR,
1342 : (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
1343 : errmsg("SCRAM channel binding check failed")));
1344 : #else
1345 : /* shouldn't happen, because we checked this earlier already */
1346 : elog(ERROR, "channel binding not supported by this build");
1347 : #endif
1348 : }
1349 : else
1350 : {
1351 : /*
1352 : * If we are not using channel binding, the binding data is expected
1353 : * to always be "biws", which is "n,," base64-encoded, or "eSws",
1354 : * which is "y,,". We also have to check whether the flag is the same
1355 : * one that the client originally sent.
1356 : */
1357 70 : if (!(strcmp(channel_binding, "biws") == 0 && state->cbind_flag == 'n') &&
1358 0 : !(strcmp(channel_binding, "eSws") == 0 && state->cbind_flag == 'y'))
1359 0 : ereport(ERROR,
1360 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1361 : errmsg("unexpected SCRAM channel-binding attribute in client-final-message")));
1362 : }
1363 :
1364 78 : state->client_final_nonce = read_attr_value(&p, 'r');
1365 :
1366 : /* ignore optional extensions, read until we find "p" attribute */
1367 : do
1368 : {
1369 78 : proof = p - 1;
1370 78 : value = read_any_attr(&p, &attr);
1371 78 : } while (attr != 'p');
1372 :
1373 78 : client_proof_len = pg_b64_dec_len(strlen(value));
1374 78 : client_proof = palloc(client_proof_len);
1375 78 : if (pg_b64_decode(value, strlen(value), client_proof,
1376 78 : client_proof_len) != state->key_length)
1377 0 : ereport(ERROR,
1378 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1379 : errmsg("malformed SCRAM message"),
1380 : errdetail("Malformed proof in client-final-message.")));
1381 78 : memcpy(state->ClientProof, client_proof, state->key_length);
1382 78 : pfree(client_proof);
1383 :
1384 78 : if (*p != '\0')
1385 0 : ereport(ERROR,
1386 : (errcode(ERRCODE_PROTOCOL_VIOLATION),
1387 : errmsg("malformed SCRAM message"),
1388 : errdetail("Garbage found at the end of client-final-message.")));
1389 :
1390 78 : state->client_final_message_without_proof = palloc(proof - begin + 1);
1391 78 : memcpy(state->client_final_message_without_proof, input, proof - begin);
1392 78 : state->client_final_message_without_proof[proof - begin] = '\0';
1393 78 : }
1394 :
1395 : /*
1396 : * Build the final server-side message of an exchange.
1397 : */
1398 : static char *
1399 66 : build_server_final_message(scram_state *state)
1400 : {
1401 : uint8 ServerSignature[SCRAM_MAX_KEY_LEN];
1402 : char *server_signature_base64;
1403 : int siglen;
1404 66 : pg_hmac_ctx *ctx = pg_hmac_create(state->hash_type);
1405 :
1406 : /* calculate ServerSignature */
1407 132 : if (pg_hmac_init(ctx, state->ServerKey, state->key_length) < 0 ||
1408 66 : pg_hmac_update(ctx,
1409 66 : (uint8 *) state->client_first_message_bare,
1410 132 : strlen(state->client_first_message_bare)) < 0 ||
1411 132 : pg_hmac_update(ctx, (uint8 *) ",", 1) < 0 ||
1412 66 : pg_hmac_update(ctx,
1413 66 : (uint8 *) state->server_first_message,
1414 132 : strlen(state->server_first_message)) < 0 ||
1415 132 : pg_hmac_update(ctx, (uint8 *) ",", 1) < 0 ||
1416 66 : pg_hmac_update(ctx,
1417 66 : (uint8 *) state->client_final_message_without_proof,
1418 132 : strlen(state->client_final_message_without_proof)) < 0 ||
1419 66 : pg_hmac_final(ctx, ServerSignature, state->key_length) < 0)
1420 : {
1421 0 : elog(ERROR, "could not calculate server signature: %s",
1422 : pg_hmac_error(ctx));
1423 : }
1424 :
1425 66 : pg_hmac_free(ctx);
1426 :
1427 66 : siglen = pg_b64_enc_len(state->key_length);
1428 : /* don't forget the zero-terminator */
1429 66 : server_signature_base64 = palloc(siglen + 1);
1430 66 : siglen = pg_b64_encode((const char *) ServerSignature,
1431 : state->key_length, server_signature_base64,
1432 : siglen);
1433 66 : if (siglen < 0)
1434 0 : elog(ERROR, "could not encode server signature");
1435 66 : server_signature_base64[siglen] = '\0';
1436 :
1437 : /*------
1438 : * The syntax for the server-final-message is: (RFC 5802)
1439 : *
1440 : * verifier = "v=" base64
1441 : * ;; base-64 encoded ServerSignature.
1442 : *
1443 : * server-final-message = (server-error / verifier)
1444 : * ["," extensions]
1445 : *
1446 : *------
1447 : */
1448 66 : return psprintf("v=%s", server_signature_base64);
1449 : }
1450 :
1451 :
1452 : /*
1453 : * Deterministically generate salt for mock authentication, using a SHA256
1454 : * hash based on the username and a cluster-level secret key. Returns a
1455 : * pointer to a static buffer of size SCRAM_DEFAULT_SALT_LEN, or NULL.
1456 : */
1457 : static char *
1458 2 : scram_mock_salt(const char *username, pg_cryptohash_type hash_type,
1459 : int key_length)
1460 : {
1461 : pg_cryptohash_ctx *ctx;
1462 : static uint8 sha_digest[SCRAM_MAX_KEY_LEN];
1463 2 : char *mock_auth_nonce = GetMockAuthenticationNonce();
1464 :
1465 : /*
1466 : * Generate salt using a SHA256 hash of the username and the cluster's
1467 : * mock authentication nonce. (This works as long as the salt length is
1468 : * not larger than the SHA256 digest length. If the salt is smaller, the
1469 : * caller will just ignore the extra data.)
1470 : */
1471 : StaticAssertDecl(PG_SHA256_DIGEST_LENGTH >= SCRAM_DEFAULT_SALT_LEN,
1472 : "salt length greater than SHA256 digest length");
1473 :
1474 : /*
1475 : * This may be worth refreshing if support for more hash methods is\
1476 : * added.
1477 : */
1478 : Assert(hash_type == PG_SHA256);
1479 :
1480 2 : ctx = pg_cryptohash_create(hash_type);
1481 4 : if (pg_cryptohash_init(ctx) < 0 ||
1482 4 : pg_cryptohash_update(ctx, (uint8 *) username, strlen(username)) < 0 ||
1483 4 : pg_cryptohash_update(ctx, (uint8 *) mock_auth_nonce, MOCK_AUTH_NONCE_LEN) < 0 ||
1484 2 : pg_cryptohash_final(ctx, sha_digest, key_length) < 0)
1485 : {
1486 0 : pg_cryptohash_free(ctx);
1487 0 : return NULL;
1488 : }
1489 2 : pg_cryptohash_free(ctx);
1490 :
1491 2 : return (char *) sha_digest;
1492 : }
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